The invention relates to an optical switching element including two optical guides arranged in parallel, which are each constituted by a strip of a semiconductor material having a first refractive index formed on a semiconductor substrate of a material having a second lower refractive index such that the light is confined in the strip forming the guide, the dimensions of these guides being such that they each transport a monomode wave and the switching operation being obtained by means of the effect of voltages applied to the electrodes arranged in the switching zone.
The invention further relates to an optical switching matrix constituted by a number NxN of these switching elements.
The invention is used for switching optical signals transported through optical fibers, for example in the telecommunication field, in which the switching between numerous optical fibres must be made possible in order to avoid that the optical signals transported through the fibres have to be converted into electrical signals during the switching between the different subscribers.
An optical switching element apt to form a switching matrix, such as defined in the opening paragraph, is known from the publication entitled "Low-loss GaAs-Ga.sub.1-x Al.sub.x As double-heterostructure directional coupler" by A. Carenco, P. Sansonetti et al in "Technical Digest", of the 7th Topical Metting on Integrated and Guide-Wave Optics", Orlando Hyatt Hotel, Kissimee, Fla., Apr. 24-26, 1984, designated by Th B 4-1.
This publication discloses a switching element constituted by two optical guides formed by strips of GaAs. These strips are arranged in parallel and are formed one beside the other at a very small relative distance at the surface of a layer of Ga.sub.1-x Al.sub.x Ax, which serves as a confinement layer between these optical guides and the flat substrate of GaAs. Another layer of Ga.sub.1-x Al.sub.x As covers each of the strips forming the guides. The latter are formed on the other hand in relief on the substrate by etching of a starting layer. Schottky electrodes are finally formed on the surface of each of the guides, while the opposite surface of the substrate is provided with a layer forming an ohmic contact.
The guides each transport a monomode wave and due to the small distance separating them laterally a polarization applied to one or the other of the guides permits of changing the coupling of the two monomode guides, thus ensuring the desired switching.
A switching matrix can be formed from such switching elements by joining the guides of an element to the guides of another element by means of curved guide portions.
However, such a structure has several disadvantages. In the first place, the lateral distance between the strips on the substrate is an extremely critical factor for the behaviour of the switching element. Now, the lateral distance between two semiconductor strips formed on a surface can be controlled only with difficulty. In the device described in the aforementioned publication, this lateral distance is of the order of 2 to 3 .mu.m. Since the coupling length, i.e. the longitudinal dimension of the optical guides, is associated with this lateral distance, this longitudinal dimension in this case is several millimeters, which is really enormous for dimension of integrated circuits.
Moreover, curved guide portions connect the switching elements to each other in order to form a matrix. These portions establish necessarily this connection at a very small angle, which results in that such a matrix occupies a very large surface area. On the other hand, the methods of etching or of epitaxial growth used to form these portions are always anisotropic, which results in that the outer walls of these portions are rough or have steps leading to losses in these portions.